The present invention relates to the field of oil and related services, and more precisely to completing wells for producing hydrocarbons, geothermal wells, or the like.
The conventional practice in the oil industry consists in fitting the well with a metal lining which is generally known as xe2x80x9ccasingxe2x80x9d, which casing is lowered down the hole and then fixed by means of cement that is placed in the annular gap between the casing and the wall of the hole. Lining the well in this way serves to prevent the walls from collapsing and also serves to isolate the various geological strata so as to avoid fluids being exchanged between them.
The casing can extend into the production zone. Under such circumstances, perforations are made through the casing and the cemented zone so as to allow fluids to flow from the formation into the well. If some of the perforations begin to produce increasing quantities of water or gas, e.g. due to the reservoir aging, it is relatively easy to plug them and to proceed with making new perforations in zones that are more favorable.
Although lining is highly advantageous in the medium or long term, it suffers in the short term from being relatively expensive, from delaying the start of production, and from limiting initial production since fluid can penetrate into the well only via the perforations and not through the entire periphery of the well where it passes through the production zone. This point is particularly critical in so-called xe2x80x9chorizontalxe2x80x9d wells, i.e. wells that are typically deviated by more than 25xc2x0 from the vertical, with the main justification for so doing being to increase the interface area between the well and the production zone.
That is why many wells, and in particular a large proportion of horizontal wells, are left open in the hydrocarbon production zone. When the formations are poorly consolidated, the walls are prevented from collapsing by a slotted liner which is merely put into place (i.e. without any cement in the annular gap).
However, as the reservoir ages, the need to control ingress of water (or gas) into the well becomes more and more critical. Unfortunately, this problem is made even more difficult to solve by the entry point of the undesired fluid into the well being difficult to locate, as is usually the case. The fluid can flow behind the slotted liner over a long distance before actually emerging in the well. Depending on the shape of the well, the entry points can be upstream or even downstream from the apparent entry point.
Independently of that difficulty in locating the source of fluid, there are few effective means for plugging such leaks. In general, the means available consist in isolating the zone to be treated by means of packers and in injecting a consolidating fluid (resin or cement) into the treated zone. U.S. Pat. No. 5,339,901 and U.S. Pat. No. 5,697,441 give examples of such techniques known in the prior art. Those techniques are satisfactory for isolating the end of a well, with the zone upstream from the plug being abandoned, however they do not make it possible to guarantee that cement is placed behind an extended length of liner as is necessary if production zones are to be found upstream from the zone that is to be treated.
Another solution consists in putting a closed liner into place and then expanding it closer to the walls of the well. Such a liner, made of composite material, plastic or metal, can then be cemented using traditional techniques. Depending on circumstances, the slotted liner is left in place or is withdrawn. The cost of such techniques is particularly high because of the cost of the liner itself and because of the techniques used for putting it into place, and in particular for expanding it.
An object of the present invention is to provide a novel method of reestablishing isolation between zones of an open hole provided with a slotted liner, in particular a borehole for exploiting a deposit of hydrocarbons, gas, water, or the like, the method consisting in pumping an isolation material from the surface to injection apparatus while providing sealing along the slotted liner downstream from the point at which the isolation material is injected so that the isolation material fills the borehole upstream from the injection apparatus together with the space behind the slotted liner, and in raising the injection apparatus towards the surface. xe2x80x9cUpstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d are defined relative to the flow of hydrocarbon, so upstream is thus a point that is closer to the surface.
The method of the invention avoids using a closed liner and the injection zone is at all times relatively small which means that it is possible to ensure that the isolation material penetrates effectively behind the slotted liner, expelling the fluids present towards the surface of the well.
The isolation material can be a resin that polymerizes after being put into place, or a cement, in particular a thixotropic cement such as a foam cement in particular. Foams based on microcement are particularly preferred, i.e. on cement in which the maximum particle size lies in the range 6 xcexcm to 12 xcexcm, and preferably in the range 8 xcexcm to 11 xcexcm, with the median particle diameter being a few microns, typically 4 xcexcm for commercial microcements, and having a specific surface area per unit weight determined by the air permeability test (Blaine fineness) in excess of 0.6 m2/g, preferably greater than 0.7 m2/g, and more preferably close to 0.8 m2/g.
The invention also provides injection apparatus particularly adapted to implementing the method of the invention and comprising: a hollow tubular body whose outer wall includes at least one ring forming a prestressed sealing gasket and a piston engaged around the tubular body and capable of being displaced along the tubular body between a rest position in which the piston compresses the prestressed sealing gasket and prevents any flow of isolation material from the injection apparatus, and an open position in which the prestressed sealing gasket is disengaged to come into contact with the slotted liner and the isolation material can flow out from the injection apparatus.
In a particularly preferred variant of the invention, the apparatus is moved by means of coiled tubing, and after cementing, the hole is rebored to the inside diameter of the slotted liner using a boring tool that is likewise mounted at the end of coiled tubing.
Other advantageous characteristics and details of the invention appear from the following description given with reference to the figures.